PC won't power down completely

Fresh install of Windows 7 for the most part but when I go to "Shut Down", windows will shut down, my monitor goes to stand by but my PC is still running. I can hear the fans running and I have to hold down the power on the tower for a few seconds for it to shut down all the way. Not a big problem as I usually just leave it on and put it to sleep when I'm down with it. Just wondering why its doing this. Thanks for any help on this.

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